Gastric and colorectal cancers are the common types of cancer in different area of the world. They are also the top leading causes of cancer death. Gastrointestinal (GI) cancers grow from the mucosal layer. Survival rates for patients suffering from these cancers may be improved if pre-malignant and early cancers are removed en bloc at an early stage before they spread to lymph nodes.
Endoscopic mucosal resection (EMR) and Endoscopic submucosal dissection (ESD) were developed for removal of pre-malignant and early cancers in the GI tract. These procedures are performed with the use of a flexible endoscope and have advantages of being minimally invasive and organ sparing. To remove larger lesions, ESD, which is associated with a lower rate of local recurrence (compared to EMR) because of a higher rate of complete resection in a single piece, is usually required.
Generally, during an ESD surgery, the margins of the lesion are marked by electrocautery, and submucosal injection is used to lift the lesion; a circumferential incision into the submucosa is performed around the lesion with specialized endoscopic electrocautery knives; and the lesion is dissected from underlying deep layers of GI tract wall with the electrocautery knife and removed. Compared to open surgery, mucosal resection performed with an endoscope is clearly less invasive.
Although ESD effectively removes early gastric and colorectal cancers, ESD is a technically demanding procedure associated with a higher risk of complications. In general, ESD mainly has three shortcomings. First, the current flexible endoscopes have a single instrument channel. Endoscopists can only operate with a single accessory at a time. Second, it is difficult to maintain the tip of a flexible endoscope in a stable position inside a hollow viscus. Targeting a mucosal lesion with a flexible endoscope can be technically challenging. Often incisions are made inadvertently resulting in major complications such as perforation and bleeding. Thirdly, large bowel ESD surgery located in the proximal large bowel (cecum and transverse colon) is more demanding to perform due to difficulty in maintaining the position of the endoscope and also a thinner muscle layer.
Surgical robots have been developed for many years. There are few robots which can be applied with the use of flexible endoscopes. Robots aim to simulate operating with two arms. This design is inspired by some animal's body structure such as human and lobster where they both use their arms and eyes to finish tasks. This design can reduce the learning curve of surgeon. Our previous work showed the preliminary design of our robot and the usability of this structure in doing ESD. Moreover, arm liked design mimics our wrists and provides more degree of freedom. This makes endoscopic dissection easier and more efficient. This concept is also adopted in our design of this robot.
The nowadays surgical robot can be divided into two categories: direct driven and motorized. The advantages of direct driven robot are low cost and simple structure. Controller and robot are connected directly by mechanical structures such as tendon and sheath. Operators control the robot through the controller. There is direct force feedback to the controller and then onto the operator. However, the drawback of direct driven robot is lack of control accuracy.
Pure mechanical structure usually has backlash and force losing problems. Robot performs different from the input of the controller. Motorized robot can solve the above problems. For example, compensatory mechanism can be used to cancel backlash and force reduction. In addition, motorized robot can have more degrees of freedom since the motion of the robot is not directly mapped with the controller. The motion of the robot can be more complex.
The current endoscopic robots have structural limitations that robot arms are embedded in the endoscope platform. When surgeon is inserting the robot into patents gastrointestinal tract, the robot arms at the tip are bulky and thus it will be difficult for them to be passed. They can potentially cause mucosal damage as they are pushed along the digestive tract. Beside the robots having a cap to protect the robot arm, the endoscope platform needs to be developed together with the robot. The cost is therefore increased.